Investigation of Some Minerals as Radiation Dosimeters

Abstract

The phenomenon of thermoluminescence (TL) now has various applications such as in radiation dosimetry, age determination and geological research. Use in geology was one of the earliest applications of TL, before the beginning of the 20th century both terrestrial and extraterrestrial (meteorite) rocks were examined for TL. Thermoluminescence is the process in which a mineral emits light while being heated. It is a stimulated emission process occurring when the thermally excited emission of light follows a previous absorption of energy from radiation. Energy absorbed from ionizing radiation (alpha, beta, gamma, cosmic rays) frees electrons to move through the crystal lattice and some of these are trapped at imperfections in the lattice. Subsequent heating of the crystal can release some of these trapped electrons with an associated emission of light. The graph of the intensity of the emitted light against the applied heat is called a glow curve. This glow curve can be considered a ‘fingerprint’ of the mineral and does not just depend on the nature of the phosphors involved, but also on the dose received in nature, that is the period over which this dose is delivered and the temperature experienced by the specimen during this time. Many minerals are naturally occurring thermoluminescent dosimeter (TLD) materials. Their characteristic TL properties depend on the type and concentration of impurities in the mineral sample (mainly rare earth elements). The location of minerals plays an important role in mineral formation and impurity concentration. Studying the TL of minerals such as quartz, feldspar and alumina has clearly indicated that TL peaks observed in glow curves are due to traps formed by irradiation and heat treatment.